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Post by LunarOrbit on Nov 3, 2010 19:37:40 GMT -4
I think that discussing with some memebers of this forum is totally impossible. They think they detain the knowledge, ignore all the arguments who are given to them, and think that whoever disagrees with them is an idiot! We are not ignoring your arguments, and we are not calling you an idiot. You need to consider the possibility that you don't know as much as you think you do and that you are wrong. What you are suggesting is that you know more about this than people who do it for a living. |
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Post by JayUtah on Nov 3, 2010 19:44:16 GMT -4
And if in this article they don't talk about the natural tendency of satellites to show the same side to the earth, it's because they think that people are familiarized with it, and don't need to be told this fact. Argument from silence. You're saying it must be true because they don't talk about it. Yet you demand references that explicitly establish a space-fixed attitude state. Have you considered that what you're asking for is also such a basic concept that it won't be mentioned? I and others explained at length what was the "natural tendency" of the spacecraft in the article you cite. You just ignored all that. You have your own private interpretation of what "flat spin" means, regardless of the inherent absurdity of it, and you're unwilling to entertain the notion that you're wrong. The natural tendency of a spinning satellite is to transfer the rotational motion to the major axis -- the axis with the greatest moment of inertia. You were even shown, using basic physics, why this occurs. As we've laboriously pointed out, you've wrongly extended that special case to include all spacecraft. The notion that a spacecraft maintains its orientation relative to the local vertical and horizontal is not an uncommon misconception. Many beginning students have the same impression. But you only have to remind them gently that Newton's first law still applies, and they -- who generally have a sufficient grasp of physics -- will invariably say, "But of course, I had forgotten." You wrongly believe you can continue to bluster your way along. You wrongly believe that your mistakes aren't characteristic of a beginning student -- and not a very good one. You wrongly believe we're all amateurs and therefor can't easily see how much you're bluffing. You don't seem amenable to the possibility that we seem entrenched because we've done the practical work to demonstrate the correctness of our understanding. Not everyone Googles to understand things. Not everyone learns only from Wikipedia. You need to get it very clear that people here aren't as stupid as you wish. |
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Post by grashtel on Nov 3, 2010 19:48:15 GMT -4
You said that in the book "From rise to earth" the author says that losing height makes the horisontal speed decrease. So, I want to see the excerpt which says that, and in which context it says that. How can I discuss on this if I don't have the reference? There can be execellent sources for free, they are not necessarily paying. As long as I have not seen the text which talks about it, I won't discuss it. When the lem descends vertically, it doesn't not lose horizontal speed; thetre is no resistance of air in space to slow it down. May be you can provide me with the excerpt which talks about it! Might I suggest some basic reading on orbital mechanics it will explain very basic things like the way that orbital speed is related to altitude and Kepler's Laws which you are very obviously ignorant of despite claiming expertise in the field. |
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Post by JayUtah on Nov 3, 2010 19:52:37 GMT -4
Of course, the orbital body can lose altitude without losing its horizontal velocity...No. That's as wrong as it can possibly be. The relationship between orbital altitude and orbital velocity is absolutely rigid. I have used this analogy, knowing it was not exact, because the lem does not behave like an helicopter, but to help people to understand.I already understand. Please stop assuming we're all less informed than you. The problem with your inexact analogies is that they are confusing you. You are the one who doesn't know what properties of the analogy hold and which don't. This is why you've got it stuck in your head that an orbiting spacecraft behaves like a toy on a string.
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Post by JayUtah on Nov 3, 2010 19:55:48 GMT -4
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Post by JayUtah on Nov 3, 2010 19:59:21 GMT -4
Thanks for the acronyms; may be the ones I use are not the good ones, but I'm used to using them, and I think that everybody understands them, even though they may not be the exact terms I should use. No. One of the sure telltales of an amateur is his unfamiliarity with standard nomenclature. He'll make up words for concepts he runs across, not knowing that those who practice those concepts in their profession already have a vocabulary to define them. We use that conventional vocabulary because we all need to understand each other. |
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Post by AstroSmurf on Nov 3, 2010 20:34:44 GMT -4
You said that in the book "From rise to earth" the author says that losing height makes the horisontal speed decrease. So, I want to see the excerpt which says that, and in which context it says that. I sincerely hope it doesn't, because the reality is of course that reducing height will increase horizontal speed. Indeed, the exact converse holds true as well - increase your horizontal speed with your prograde burn, and your altitude will increase, decrease it using a retrograde burn and the altitude will decrease, all by itself. No attitude change is necessary until the spacecraft has slowed to far below orbital speeds, in which case you can switch your computations to ballistic ones for simplicity. My personal reference is "Fundamentals of astrodynamics", Roger R. Bate, Donald D. Mueller and Jerry E. White, Dover Publications, New York 1971. A trifle old, and very focused on ballistics, but pretty comprehensive. Plus, it has a nice photo of the LM in lunar orbit on the cover  I found it for about £5 at an astronomy meeting. |
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Post by echnaton on Nov 3, 2010 20:41:29 GMT -4
It does not disprove what I said. Some satellites need an attitude control because their natural attitude does not allow them to point exactly to a given point on the earth. You claim the Apollo CSM was not one of these satellites. Yet every question I have put to you to get you to say exactly what it is about the CSM that gives it the properties you claim it to have and to differentiate it from other possible object in orbit have has been answered with vague hand waving or inapplicable analogies. How about providing some calculations or sources that agree with you. |
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Post by randombloke on Nov 3, 2010 20:45:17 GMT -4
Inquisitivemind:
A practical experiment for you, in the vein of your flawed string analogy. You will need that same string and rock, as well as a suitably sized triple-gimbal bracket (such items can be found in many "office" or "desk" toys).
Mount your rock (which preferably has a distinct major axis) to the gimbal in such a way that it may rotate freely about its centre of mass.
Now attach the outermost ring of your gimbal to the string and swing the whole arrangement about your head as before, paying attention to the orientation of the major axis of your rock.
Is it parallel or perpendicular to your noggin?
Come back when you have an answer please.
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Post by Tanalia on Nov 3, 2010 20:57:25 GMT -4
Add helicopter operations to the list of things of which IM is clueless.
While a helicopter can fly either landing he pictured, neither approach would be used unless required to avoid obstacles. A normal approach is along a straight line, emulating a gliding airplane, with the exception that approach speed and descent rate are reduced together so you basically end in a hover. Either of his pictured approaches has a strong vertical descent, which is to be avoided when possible -- there is a condition referred to as a vortex ring state (aka "setting into its own downwash") which can occur in a rapid vertical descent, and breaking it requires horizontal motion, defeating the original intent. Avoiding it for vertical descent thus requires going slowly, actually using more fuel, since you have to almost hover in midair (which is much less efficient than hovering above the ground, due to lack of ground effect).
Fuel economy is not the main concern, safety is. If you wanted an economy landing, you'd just close the throttle to idle and autorotate (glide) down, only applying power again to transition to a hover at the end (or not, and just landing directly without power). But this is considered an emergency maneuver -- the craft is not slowing down as with a normal descent, and without power your options can become very limited if something unexpected happens.
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Post by echnaton on Nov 3, 2010 20:58:45 GMT -4
Anyway, I perfectly know that I won't convince you, and that I'll remain an ignorant idiot for you. But it's reciprocal, you'll never convince me either! I have no formal study in science beyond high school and no training at all. But I have read about physics and space travel for many years and all sources I have encountered disagree with you. Why should I throw all that education away based on your analogies? The purpose of this board is to document hoax claims and point out the flaws. We do that by challenging hoax proponents as much as possible to get them to reveal the details of their claims and the extent the knowledge they possess. Then the claims can be fairly rebutted. So far your willingness to participate has been very helpful in meeting the goals of the board. There is no expectation your mind will be changed. |
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Post by slang on Nov 3, 2010 21:01:59 GMT -4
I need to know what I'm talking about. Well, Gargleplatz, that didn't stop you from publishing your ridiculously flawed understanding of early computer architectures. Thanks for that, though. It provided for a great laugh. |
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Post by Apollo Gnomon on Nov 3, 2010 21:42:26 GMT -4
Am I right in thinking that, judging by this response, the only sources you will consider valid for research are free, probably online, sources? What about textbooks on the various subjects being mentioned here, that you can't read without purchase or loan? You said that in the book "From rise to earth" the author says that losing height makes the horisontal speed decrease. - that's not what he said. Lowering orbital height does not decrease orbital speed. Decreasing orbital speed does not decrease orbital height. That's one of the many reasons why difficult things are compared to "rocket science." Things in orbit are different than your terrestrial/ aeronautical experiences have taught you. You don't need a specific reference to know that your statement above is utterly wrong. There is no way for an orbiting object to "descend vertically" that involves maintaining horizontal velocity. In fact, you're going to INCREASE horizontal velocity to lower your orbit height. Really. It's counter intuitive, and that's why you should go do your homework. "ORBITAL SPEED A satellite in orbit moves faster when it is close to the planet or other body that it orbits, and slower when it is farther away. When a satellite falls from high altitude to lower altitude, it gains speed, and when it rises from low altitude to higher altitude, it loses speed. A satellite in circular orbit has a constant speed which depends only on the mass of the planet and the distance between the satellite and the center of the planet. Here are some examples of satellites in Earth orbit: "  www.freemars.org/jeff/speed/index.htm |
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Post by PhantomWolf on Nov 3, 2010 22:26:11 GMT -4
It's really difficult to discuss with people who have hard anchored conceptions. Anyway, I perfectly know that I won't convince you, and that I'll remain an ignorant idiot for you. But it's reciprocal, you'll never convince me either!Need I say more? |
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Post by sts60 on Nov 3, 2010 22:56:02 GMT -4
Hello inquisitivemind, I have to complement you on your diligence in making pictures to illustrate your claims.
Unfortunately, your basic understanding of the relevant concepts is wrong. Spacecraft in general don't naturally maintain their attitude with respect to the body they're orbiting the way you think. I speak from both experience and education; I am a space systems engineer with 19 years in the business, and yes, I majored in physics before that.
I've worked on, and actually controlled, spacecraft in orbit around the Earth, including one (on three different flights) which did maintain its primary axis aligned with the orbital velocity vector in the way you think is natural. It's not. It took active attitude control with reaction wheels and magnetic torquers to maintain that.
I just came to this thread, and I don't think there's much to say beyond the explanations that have already been provided to you at this point, so I just thought I'd add a lesson from actual experience in the field. I don't "think [you're] an idiot"; you're just clinging to a rather common misconception.
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I found it for about £5 at an astronomy meeting.
